E. J. Dean, P. D. Dresselhaus, A. H. Miklich, J. X. Przybysz and A. H. Worsham
Abstract - It is a well held tenet of SQUIDs that they are only useful for measuring magnetic field changes; any attempts to measure absolute magnetic field strength are made ambiguous due to the periodicity of the SQUID V-phi curves. We have developed an array of SQUIDS that has resolved this ambiguity. Making reasonable assumptions about the external field that the SQUID is exposed to (for instance, the field under most circumstances is not expected to exceed the Earth’s field of ~0.5G) enabled us to determine the periodicity values needed for the SQUIDS in the SQUID array. The largest periodicity SQUID that has an appreciable shift in its V-phi curve thus determines the external magnetic field present. We have used this array to determine the residual field that our superconducting circuits are exposed to before (as much as 30 mG) and after (~1.5 mG) degaussing our mu-metal shielding cans.
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